Various types of drilling tools including, but not limited to, rotary drill bits, reamers, core bits, under reamers, hole openers, stabilizers, and other downhole tools are used to form wellbores in downhole formations. Examples of rotary drill bits include, but are not limited to, fixed-cutter drill bits, drag bits, polycrystalline diamond compact (PDC) drill bits, matrix drill bits, and hybrid bits associated with forming oil and gas wells extending through one or more downhole formations.
Matrix drill bits are typically manufactured by forming a main body having a plurality of blades. Each of the blades may be provided with a plurality of recesses that may be referred to as cutter pockets, each for receiving a respective cutter. The actual cutters are formed of a polycrystalline diamond (PCD) structure (interchangeably referred to as a disc or table), which is attached to a cemented carbide substrate, which is typically formed of a cemented tungsten carbide material. The complete structure of the diamond table together with the substrate to which it is attached may be referred to as a polycrystalline diamond compact (“PDC”), in that such a structure may be formed by compacting in a press at high temperature and pressure. The cutters are attached to the blades of the drill bit main body in the sockets, thereby positioning the cutters at carefully predefined locations and orientations with respect to the bit body for subsequently engaging a formation during use. It is the PCD tables which actually come into contact with, and cut through, the subterranean rock formation being drilled. The mechanical and heat stresses created via the drilling process put a significant strain on the PCD tables as well as the bond between the PCD table and the associated substrate.
Typically, the PCD tables are formed by placing diamond powder into a mold with a cemented carbide substrate and subjecting the mold to a high-pressure, high-temperature (HPHT) press cycle. The metal-solvent catalyst (typically cobalt) from the cemented carbide substrate infiltrates into the polycrystalline diamond to create diamond-to-diamond bonding as well as anchoring of the substrate to the PCD table being formed. A by-product of this process is that some of the metal-solvent catalyst remains in the interstitial spaces formed between the diamond-to-diamond bonds. These residual catalysts can have a detrimental effect on the thermo-mechanical integrity of the cutting element at the working surface since there is coefficient of thermal expansion mismatch between diamond and metal catalyst by an order of magnitude. The PCD table is then typically subjected to acid leaching to remove the metal-solvent catalyst from these interstitial spaces. The leaching process, which generally seeks to remove the metal-solvent catalyst from the entire PCD table, can often take days to weeks to complete